Apparatus for reducing the thickness of metal

ABSTRACT

Method and apparatus for reducing the thickness of metal in which a pair of freely rotatable work rolls disposed on opposite sides of the metal are oscillated in synchronism upon a pair of oscillatable arms to subject the metal to rolling action of the arms, and in which auxiliary load-applying means are included to influence the roll displacement force at particular positions of arm oscillation so as to urge the work rolls towards straight line parallel movement.

United States Patent Inventor Karel Saxl Sutton Coldfield, England Appl. No 774,416 Filed Nov. 8, 1968 Patented July 6, 1971 Assignee Imperial Metal Industries Kynoch Limited Wilton, Birmingham, England Priority Nov. 9, 1967 Great Britain 51 102/67 APPARATUS FOR REDUCING THE THICKNESS OF METAL 13 Claims, 9 Drawing Figs.

11.8. CI 72/189, 72/240 Int. Cl B21b2l/00, 1321b 31/20 Field of Search 72/217,

[56] References Cited UNITED STATES PATENTS 3,143,010 8/1964 Saxl 72/240 3,357,223 12/1967 Tremblayr. 72/189 3,425,253 2/1969 Saxl 72/240 X Primary Examiner-Milton S. Mehr Attorney-Cushman, Darby & Cushman ABSTRACT: Method and apparatus for reducing the thickness of metal in which a pair of freely rotatable work rolls disposed on opposite sides of the metal are oscillated in synchronism upon a pair of oscillatable arms to subject the metal to rolling action of the arms, and in which auxiliary load-applying means are included to influence the roll displacement force at particular positions of arm oscillation so as to urge the work rolls towards straight line parallel movement.

PATENTEU JUL-6 I97:

SHEET 1 OF 7 PATENTEU JUL-6 |97| SHUT 2 OF 7 PATENTEU JUL-5 Ian SHEET 3 BF 7 PATENTED JUL-6 Ian SHEET U U? 7 in UE PATENTED JUL-6 I97! SHEET 5 BF 7 FIG.

PATENTEU JUL-BIHTI 359E521 SHEET 6 BF 7 APPARATUS FOR REDUCING THE THICKNESS 01F METAL BACKGROUND OF THE INVENTION:

1. Field of the Invention This invention is concerned with apparatus for reducing the thickness of metal.

2. Description of Prior Art In the specification of our US. Pat. No. 3,143,010, there is described a method of reducing the thickness of metal which comprises advancing the metal between and beyond a pair of freely rotatable work rolls disposed on opposite sides of the metal, and subjecting the metal to the rolling action of the pair of freely rotatable work rolls, the rolls moving in synchronism in pendulumlike manner at high speed and effecting reduction in both directions of their movement.

This method is performed upon apparatus comprising a frame, a pair of arms oscillatable about pivotal axes, the arms having freely rotatable work rolls mounted on their free ends, which lie closer together than their pivotal axes, and mechani cal driving means operable so as to cause oscillation of the arms in synchronism with each other.

in use of the above method and apparatus, the speed of the work rolls during oscillation is at least five times the advance speed of the metal after reduction which may, for instance, lie between 30 and 150 feet per minute. it is found that using the above method and apparatus, metal may be reduced in thickness by very large amounts, without preheating and in single pass. For instance, after being reduced by a single pass, metal may have a thickness which is only 10 percent or less of its original unreduced thickness. However, in practice, while such large reductions are possible, as the rolls move between their limits of oscillation in engagement with the metal and in a direction opposite to that of the direction of advance of the metal, the metal exerts an increasing rolling load upon the rolls. This increasing load has a component which also increases and imposes an increasing strain upon the rolls and upon their supporting system so that, as the rolls move in said oppositedirection, they are forced to depart, in a direction away from one another, from their theoretical arcuate paths of oscillation at constant radius about their axes of oscillation, which arcuate paths they would follow it there was no such component of rolling load. n the return movement of the rolls, the metal exerts a decreasing component of rolling load upon the rolls. The rolls are, therefore, subjected to a decreasing strain and approach their theoretical arcuate paths of oscillation.

The component of rolling load which causes the rolls to depart from their theoretical paths of oscillation in a direction away from one another will hereinafter be referred to as the roll displacement force."

It is sometimes found that the displacement of the rolls from their theoretical paths caused by the roll displacement force, results in the finished rolled metal having rolled surfaces which are more flat than they would otherwise be if the rolls had followed their theoretical paths. This is because, under suitable circumstances of the speed of advance of a given metal, the ratio of the advance speed to the speed of roll oscillation, and distance of limit of oscillatory movement of the rolls (taken in the direction of metal advance) on the metal outgoing side of a common plane extending through the pivotal axes of the arms, the roll displacement force varies to cause the rolls on this side of the plane to follow paths which tend towards the straight-line parallel relationship. The rolled metal has, in consequence in this case, a gauge which varies to a lesser degree than would be expected if the rolls had followed their theoretical arcuate paths.

It is an object of the present invention to provide apparatus having oscillatable arms in which work roll movement may be more accurately controlled so as to conform more closely to a straight-line parallel relationship during arm movement towards the common plane and in the direction opposite to the direction of advance of the metal.

SUMMARY OF THE lNVENTlON According to the invention, apparatus for reducing the thickness of metal comprises a frame, a pair of oscillatable arms, each pivotally mounted about a pivotal axis upon the frame, the arms having free ends which lie in closer relationship than their pivotal axes, a freely rotatable work roll mounted on the free end of each arm, driving means for oscillating the arms in synchronism through a common plane in which the pivotal axes lie and for a distance on each side of said plane, and means for applying an auxiliary load to at least one member of the apparatus through which roll displacement force is applied so as either to assist or act against the roll displacement force during arm oscillation, said means being actuable to apply or vary said load or both dependent upon the oscillatory position of the arms on the outgoing side of the common plane in relation to the direction of movement of metal between the rolls, whereby during at least part of the oscillation of the arms to reduce thickness of metal on said side of the plane, as the roll displacement force alters, said means is actuated to apply or vary the auxiliary load so as to urge the work rolls towards a straight-Ilineparallel movement.

it is preferable that said means is actuable during oscillation of the work rolls in a direction opposite to that of the direction of advance of the metal as the work rolls move towardsthe common plane of the pivotal axes, as it is during this part of the oscillatory movement (referred to hereafter as the metalfinishing part of each oscillation) that final reduction in thickness of the metal takes place before it is advanced to a position beyond the reach of the rolls.

The direction of application of the auxiliary load depends upon the cyclic gauge variation of reduced metal which depends upon the paths of movement of the work rolls on the metal-finishing parts of their oscillations. For instance, it may be required that the means be actuated to apply the auxiliary load in the direction opposite to that of the roll displacement force to reduce locally the metal thickness at its otherwise thicker reduced portions so as to provide less variation in gauge. However, in normal circumstances, this result is achieved by applying the auxiliary load in the same direction as the roll displacement force.

In one preferred construction in which the auxiliary load is applied in the same direction as the roll displacement force, each arm is pivotally mounted about its pivotal axis between two beams of the frame, and each beam is pivotally mounted to a rigid framework about an axis extending transversely of the direction of feed of metal and at a position spaced in the direction of feed from the pivotal axis of the arm so as pivotally to move upon change in roll displacement. In this preferred construction, a screwdown device acts at another position of each beam and the rigid framework, and the means for applying an auxiliary load comprises fluid-operable cylinder and piston means for applying an auxiliary load to assist the action of the roll displacement force upon each beam.

In one arrangement of the preferred construction, the cylinder and piston means comprises two cylinder and piston assemblies each disposed between opposing beams of the arms so as to apply an auxiliary load between the arms to assist in pivotally moving them apart. This arrangement may be provided upon apparatus which also includes means for increasing and decreasing the stiffness of the apparatus as described in our US. Pat. No. 3,425,253.

The invention also includes a method of reducing the thickness of metal which comprises passing the metal between two work rolls freely rotatably mounted upon the free ends of a pair of oscillatable arms which are pivotally mounted about pivotal axes one on each side of the metal pass line with their free ends and thus the work rolls in closer relationship than the pivotal axes of the arms, oscillating the arms in synchronism through a common plane in which the pivotal axes lie during passage of the metal between the work rolls so as to subject the metal to rolling action of the work rolls and thereby reduce the metal thickness, and applying an auxiliary load so as either to assist or act against the roll displacement force during arm oscillation, the auxiliary load being applied I or varied dependent upon the oscillatory position of the arms on the outgoing side of the common plane in relation to the direction of movement of metal between the rolls, whereby BRIEF DESCRIPTION OF DRAWINGS Embodiments of the invention will now be described by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic side elevational view of apparatus forming a first embodiment;

FIG, 2 is a side elevational view, partly in cross section, of part of the apparatus of FIG. 1; v

FIGS. 3a and 3b are cross-sectional views of part of the apparatus of FIG. 2 and on a larger scale;

FIGA is a view, partly in cross section of fluid pressurizing and operating means of the apparatus;

FIG. is a cross-sectional view, similar to FIG. 3, of part of the apparatus showing different relative positions of the parts during operation;

FIGS. 6 and 7 are diagrammatic views, not to scale, of metal being reduced, respectively, on prior apparatus not according to the present invention and apparatus according to the present invention;

FIG. 8 is a side elevationsl view similar to FIG. 2 and of a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment, apparatus for reducing the thickness of metal consists of a rolling mill which is basically of similar construction to apparatus for reducing metal thickness as described in the specification of our US. Pat. No. 3,143,010.

The mill, with particular reference to FIGS. ii and 2, basicslly comprises a pair of pendulum arms 1 and 2, each pivotally mounted between a pair of arm-carrying beams 3 of the mill frame about u pivotal axis 4 located intermediate the beam ends. One beam 3 ofthe one pair only is shown in FIG. 2. The two axes of the two arms are disposed one directly above the other. A part of each arm oxtends'trom its pivotal axis towards the other arm to terminate in an and of the arm opposing that of the other arm. Each of the opposing ends is provided with a work roll 5 freely rotatably mounted thereon with its axis parallel to the pivotal axis and a plurality of supporting or backup rolls 6 for the work roll. The arms oscillate about their axes on both sides of a pass line A-A to move the work rolls in synchronism alternately in direction of feed of the metal and then in the opposite direction with the axes of the work rolls extending in a direction normal to the pass line. Driving means is provided for oscillating each arm, the driving means comprising a connecting rod 7 plvotnlly mounted at one end 8 of the arm and st its other end to,s crankshaft 9 which is drivable about pivot 90 by c drive motor and gearing (not shown).

During use of the mill to reduce the thickness of metal iii) (FIG, 1), as the arms oscillate the motel exerts a rolling loud upon the work rolls. A component of rolling load acts along the arms and this component fluctuates during each oscillation of the arms and the magnitude of tho component of rolling load at any instant is dependent partly upon the direction of movement of the arms at that instant and partly upon their angular position relative to the pass line of the metal.

The fluctuating component of load in each arm is taken through the associated beams 3 of the arm into a rigid framework it of the mill and for this purpose, bosms of such pair are pivotally mounted at one end 3a about a common axis to the rigid framework, the common axis extending transversely of the direction of feed of metal along the pass line. The other end of each beam is free and is operably engaged by a screwdown load device 12 through which a fluctuating roll displacement force is to be transmitted.

As shown in FIG. 3, each device 12 comprises a screwthreaded hollow shaft 13 and a screw-threaded nut 14 received around the shaft. The nut is keyed to a wheel 15 of a worm and wheel gear, so as to rotate with the wheel when it is driven by the'worm 16 by means not shown and thus move the shaft vertically to adjust the relative positions of oscillatory paths of the work rolls. The lower end of the shaft 13 is shrouded by a cup 17 which is provided with a dependent projection 1% having a lower convex surface which is pivotally seated within a recess 19 at the free end of its associated arm 3. The nut 14 and wheel 15 are located within a recess in a part of the framework ill by means of a retaining plate 20 which is held in position by nuts and studs 21. During rotation of the nut and wheel, the wheel is held in contact with a surface 22 of the framework by the retaining plate and the nut is held in sliding contact with a load-carrying sleeve 23 which surrounds the-shaft. The sleeve is prevented from rotating relativeto the framework by a key 24. The load is transferred from the hollow shaft through the nut to the sleeve 23 and from there to an annular load cell 25, which also surrounds the shaft 13, and into the framework 11 through a retaining sleeve 26 and retaining plate 27 and studs which are disposed in a pitched circle around the axis of the shaft i3.

EAch of the studs 28 is a load safety member in which each stud is preloaded in tension by nuts 2b screw-threadably received at the ends of the studs so that a reduced diameter portion 30 between stud ends is tensioned between the screwthreaded larger diameter ends. Further studs 31 located around a pitch circle surrounding the pitch circle of the studs 28 pass through the plate 27 and into the framework. These studs carry locking nuts 32 spaced slightly from the plate 27 to act as a stop in the event of the studs 28 breaking under load thereby to limit the movement of the part of the framework supporting the scrcwdown device away from the pass line A-A.

Each screwdown device 112 also incorporates means for in crossing and decreasing the stiffness of the apparatus as described in our U.S. application Scr. No. 530,615 now US. Pat. No. 3,425,253. This means comprises in this instance a single titanium tubular member 33 which is disposed axially within the shaft 13 and abuts at its and remote from cup 17 against a stop nut lid which is screw-thrsndnbly received within the upper end of the shaft 113. The other end of the tu bular member abuts against a shoulder provided upon a load carrying sleeve 35 which is slidably received in sleeve bearings 36 within the shaft R3. in use, as the work rolls oscillate on the arms in the direction opposite to the metal feed and on the outgoing side of the common piano, the increase in roll displacement force urges the work rolls apart. initially the sleeve 35 projects below the lower and of the shaft 13 so as to abut against the base of the cup 17 thereby leaving the base of the cup and tho shalt 13 slightly spaced apart. As described in U.S. application Sor. No. 530,615, therefore, the roll displacemont force urging the work rolls apart effects pivotal move mom of the beams 3 about their axes 3s and away from the pass lino thereby transmitting the roll displacement force through the projection 18 and cup 17 to each screwdown device and through the sleeve 55 into the tubular member 33. The load displacement force is then transferred from the tubu" lsr member 33 into the framework ll by means of the nut 34, shaft l3, nut id, sleeve 23, load cell 25, sleeve 26, plate 2'7 and studs 2b. The roll displacement force is initially taken, therefore, solely through the tubular members 33. However, as the tubular members are axially compressed under the increasing load, the sleeve 35 moves axially upon shah 13 until the shaft engages the base oiths cup 1'7 as shown in FIG. 5. At this point, the stiffness oi the machine becomes increased because when the shaft 13 engages the base of the cup 17, the roll displacement force is taken not only directly through each tubular member 33 but also directly through its surrounding shaft from the cup il7.

it is found in practice, however, that while the use of the stiffness increasing and decreasing means is effective in reducing the variation in uniformity of thickness of reduced metal 10, a certain degree of variation is still apparent. To illustrate the effect of apparatus incorporating stiffness increasing and decreasing means, H6. 6 is now referred to. As shown in that F 16., as the work rolls oscillate during reduction of the thickness of metal W, a metal-finishing part of each oscillation upon each incremental length 38 occurs upon work roll movement in a direction opposite to that of the metal advance and towards the common plane indicated by line 37. The metalfmishing part of an oscillation is shown diagrammatically to occur between positions 39 and d (P16. 6) which are spaced from the common plane. it is found, however, that as the work rolls move on the metal-finishing part of each oscillation, the operation of the tubular members to increase the stiffness of the apparatus directs movement of the work rolls so that they move along slightly curved paths whereby a curved surface dil is apparent upon both sides of each incremental length. As is shown by FIG. ti, as each incremental length is then fed forward the result in the finally reduced metal is a series of curved connected parts ill of the surfaces of the metal. It is found in practice that in the finished reduced strip, the thickness of the reduced metal may vary by possibly 0.00i inch between the peaks 41 2 connecting adjacent curved parts of the surfaces and the lowest regions of those parts.

To overcome this problem apparatus according to the present invention is provided with means for applying an auxiliary load to assist the action of the roll displacement force during the initial compression of the tubular members 33, i.e. before the stiffness of the apparatus has been increased to its maximum so as to decrease or eliminate completely the curvature of the surface tilt of each incremental length 38. Means for applying the auxiliary load in this embodiment is partly incorporated with each screwdown device and comprises cylinder and piston means. As shown in FIG. 3, the cylinder is provided by the nut L l-t which has a chamber 43 receiving a piston 4 41 provided with a tie rod 45 which extends axially along the tubular member 33, the other end of the tie rod having an enlarged head 46 which engages with a shoulder l7 upon the inner surface of the sleeve 35. Movement of the piston vertically by the application of fluid pressure into the chamber 43 will, therefore, subject the tubular member 33 to an axial compressive load between the sleeve 35 and nut 34.

The means for applying the auxiliary load also comprises fluid-pressurizing means to apply pressure within the chamber 43 to effect movement of the piston in a controlled manner, the fluid-pressurizing means comprising a pump db (see Fit}. 4). The pump comprises a cylinder 19 containing a piston 50, and the chamber 511 of the cylinder is interconnected directly by way of a passage 52 with the chamber d3 of the nut 3d. The piston St is urged outwardly from the cylinder by a compression spring 53 which acts against an enlarged head 54 of the piston so as to hold the remote surface of the head in engagement with a cam surface of a cam 55, which forms part of an operating means for the pressurizing means. The cam is secured to a shaft 56 which is drivable connected to the driving means of the apparatus so as to synchronize the movement of the piston with the oscillatory movement of the arms ll. Means are provided for adjusting the operation of the pressurizing means to occur at any of a plurality of oscillating positions of the arm. This means comprises a manually controlled gearwheel 57 which engages an arcuate toothed quadrant $8 secured to the cylinder 49. The quadrant b is retained in position by guide wheels 59 engaging on a bacltplate 60 of the quadrant so that the quadrant 5d and thus the cylinder d9 move upon rotation of the gear 57 around an arc, the center of which coincides with the center of rotation of the shaft ss. Rotation of the gear 57, therefore, to move the pump in either direction from the position shown in FIG. 4 will have the effect of delaying or advancing the operation of the pump by the earn as it rotates.

in use, the operation of the pump to cause the piston 44 to move to apply a compressive a'zriliary load to each of the tubular members is adjusted in an attempt to eliminate the curvature of the surface of each incremental length 38 of metal as it passes between the work rolls. In practice, it is found that the roll displacement force as it increases during movement of each work roll on the metal-finishing part of each oscillation is initially taken through the tubular members 33 as described above. At a predetermined position of the work rolls between the position 39 and tilt the pump, which has previously been set in a most desirable position by the gear 5'7, is caused to operate so as to effect movement of the piston along the cylinder to apply an auxiliary load to the tubular members. This auxiliary load has the effect of assisting the roll displacement force in moving the work rolls apart from one another so that if the auxiliary load is applied before the work rolls reach their closest relative positions apart on the metalfinishing part of each oscillation, then the work rolls are caused to continue on their oscillation further apart than they would otherwise have done. The effect of this is shown diagrammatically in FIG. 7 from which it is clear that if the curvature of the surface dl upon each incremental length 38 is not removed completely, then at least the curve is less pronounced and the variation in metal thickness is clearly reduced so that the work rolls move more towards straightline parallel paths along their metal finishing parts of the oscillations.

In practice, it may be desirable to commence operation of the apparatus and then to adjust the position of operation of the pump it? depending upon the results achieved upon the reduced strip. For instance, it may be found that if the varia tion in reduced thickness is unsatisfactory, this may be because the auxiliary load is being applied at a slightly incorrect position of work roll oscillation between positions 39 and d ll and that more uniformity of thickness may be obtained by either advancing or retarding the operation of the pump slightly.

in a modification of the first embodiment (not shown) means are provided for adjusting the working volume of the pump to adjust the auxiliary load. This means may comprise a linkage mechanism between the cam and piston, the effective working length of one of the links being adjustable so that the ratio of compound movement is changed to alter the length of stroke of the piston. Such a type of linkage is well known in the engineering field. Clearly, this effect may be achieved by other means, for instance, by having the cam surface on the outside of an eccentric annulus which itself is angularly adjustably mounted around a second eccentric annulus which is fixed upon the cam drive shaft. By altering the angular position of the outer annulus, the effective eccentricity of the outer annulus can be varied, thereby altering the effective working stroke of the piston.

In a second embodiment as shown in FIG. h, apparatus for reducing the thickness of metal is basically of the same construction m described in the first embodiment and identical parts bear identical reference numerals. in this embodiment, however, although each screw down mechanism 12 is of the hollow screw shaft and nut construction driven by a worm and worrnwheel as described in the first embodiment, no means for providing an auxiliary load is provided upon each screw down device. in this particular case, the tubular member 33 of each screw clown device does not, therefore, contain a tie rod and as the piston dd is omitted, the nut at the end of the shaft i3 is of solid construction. In contrast, in the present embodiment, a means for applying an auxiliary load is two fluidoperablc means, each of which are disposed between the free ends of opposing beams ll of the mill as. shown in FlG. 8. One of these means only is shown. Each fluid operable means comprises a cylinder bl, a chamber of which contains a piston 62, extensions of the cylinder and piston being pivotally mounted respectively at the free ends of upper and lower beams. Fluid is provided for pressurizing the chamber in the cylinder 61 from an accumulator 63 so that upon altering the relative positions of upper and lower beams prior to operation of the mill, a desired pressure within the chamber may be maintained although the volume of the chamber is altered. A part 64 of a passage 65 connecting the accumulator with the chamber is of restricted cross-sectional area, as shown diagrammaticallyin FIG. 8, so as to allow for the flow of fluid through the restricted part in both directions at a rate which is slow relative to that normally required to cause movement of the piston within the cylinder to apply an auxiliary load during a working operation. The restricted part 64, therefore, ensures that the accumulator may only be used to apply fluid to or remove it from the chamber by the operation of the screw down mechanism when a slow flow of fluid is allowed to take place. A bypass 66 of the passage is connected to a fluid-pressurizing means which is drivable by an operating means. The fluidpressurizing means and the operating means are of the same construction as described in the first embodiment with reference to FIG. 4.

in operation of the mill as described in the first embodiment, the roll displacement force increases as the work rolls move from positions 39 to on the metal-finishing part of each oscillation. During this part of each oscillation, the pump 48 of the operating means is operated so as to pump fluid into the chamber of the cylinder 6i whereby the piston 62 is moved outwardly from the cylinder to impart an auxiliary load to assist the roll displacement force acting on the screwdown devices 12. As described in the first embodiment, the position of application of the auxiliary load may be adjusted by movement of the pump 48 around the axis of the driving shaft 56 so that the most effective position is obtained to ensure that each reduced incremental length 38 of strip has the greatest uniformity of thickness possible by controlling movement of the work rolls on the metal-finishing part of each oscillation so that they move from their otherwise arcuate paths towards or into straight-line parallel paths of movement.

lclaim:

1. Apparatus for reducing the thickness of metal comprising a frame, a pair of oscillatable arms, each pivotally mounted about a pivotal axis upon the frame and one on each side of pass line for metal, the arms having free ends which lie in closer relationship than their pivotal axes, a freely rotatable work roll mounted on the free end of each arm, driving means operably connected to the arms to oscillate the arms in synchronism through a common plane in which the pivotal axes lie and for a distance on each side of said plane, wherein the improvement comprises auxiliary load-applying means operably connected to apply an auxiliary load to at least one member of the apparatus through which roll displacement force is applied, to influence the roll displacement force during arm oscillation, said means being actuable to influence the roll displacement force, dependent upon the oscillatory position of the arms on the outgoing side of the common place in relation to the direction of movement of the metal between the rolls, thereby to cause the work rolls to be urged towards straight-line parallel movement as the roll displacement force alters during at least part of the arm oscillation on said side of the plane.

2. Apparatus according to claim I wherein the means for applying an auxiliary load comprises a fluid-operable means.

3. Apparatus according to claim 2 wherein the fluid-operable means comprises a cylinder and piston assembly which is operably connected to parts of the apparatus, the cylinder and piston being relatively movable upon operation to apply the auxiliary load, and wherein fluid-pressurizing means is provided having an operating means, the fluid pressurizing means being operably connected to the cylinder and piston assembly to vary the fluid pressure acting within the cylinder upon operation of the operating means.

4. Apparatus according to claim 1 wherein on each side of the pass line, the frame has two beams upon which an oscilbeam, a screw down device is provided which acts at another position of the beam between the beam and the rigid frame work, the auxiliary load-applying means comprising a fluidoperable cylinder and piston means operable to assist the action of the roll displacement force upon each beam, fluid-pressurizing means operably connected to the cylinder and piston means to vary fluid pressure acting within the cylinder, and operating means operably connected to the pressurizing means to actuate the pressurizing means.

5. Apparatus according to claim 4 including means for increasing and decreasing the stiffness of the apparatus and thereby the resistance to displacement of the rolls away from their theoretical paths of oscillation, such displacement being caused by roll displacement force, said means being operable to increase stiffness during movement of the rolls towards said plane and in a direction opposite to that of the direction of feed of metal to be passed between the rolls, and being operable to decrease the stiffness during movement of the rolls away from said plane and in the direction of metal feed, and wherein the fluid-pressurizing means is actuable by the operating means to cause an application of or increase in the auxiliary load before the stiffness of the apparatus has been increased to its maximum by operation of the stiffness increasing and decreasing means.

6. Apparatus according to claim 5 wherein with regard to each beam the stiffness increasing and decreasing means comprises at least one tubular member located so as to be subjected to roll displacement force during arm oscillation, increase in the roll displacement force causing pivotal movement of the beam accompanied by axial compression of the tubular member, and in which the cylinder and piston means are disposed so as to apply an auxiliary load to assist in the axial compression of the tubular member.

7. Apparatus according to claim 6 wherein the screw down device comprises a screw-threaded hollow shaft and a screwthreaded nut received around the shaft, and wherein the tubular member is disposed axially within the shaft to axially receive the whole of the roll displacement force acting through the beam which then passes into the hollow shaft and under a certain degree of axial compression of the tubular member of the roll displacement force is transmitted directly into the tubular member and also into the hollow shaft to increase the stiffness of the apparatus, and the cylinder and piston means comprises a piston received within a cylinder which is disposed at one end of the tubular member, the piston having a tie rod extending along the tubular member and being operable upon the other end of the tubular member to apply an auxiliary load to assist in the axial compression of the tubular member while the whole of the roll displacement force is transmitted through the tubular member and then into the hollow shaft.

8. Apparatus according to claim 4 wherein each beam of each arm lies in opposition to a beam of the other arm and the fluid-operable cylinder and piston means comprises two cylinder and piston assemblies each disposed between opposing beams of the arms to apply an auxiliary load between the arms to assist in pivotally moving them apart.

9. Apparatus according to claim 8 wherein an accumulator containing fluid is connected with the interior of the cylinder of each assembly to maintain a desired pressure within the cylinder before the application of auxiliary load in the event of voliometric change within the cylinder caused by adjustment in operating positions of parts of the apparatus.

l0. Apparatus according to claim 2 wherein the operating means comprises a cam operably connected to the fluid-pressurizing means, the cam being secured to a rotatable shaft drivable by driving means. I

- 11. Apparatus according'to claim 10 wherein means are provided for adjusting the operation of the fluid-pressurizing means to occur at any of a plurality of oscillatory positions of the arms.

12. Apparatus according to claim 11 wherein said means for adjusting the operation of the fluid-pressurizing means comprises a gear means which is operably connected to the fluidpressuri zing means to alter its angular position relative to the axis of rotation of the cam whereby the operation of the fluidpressurizing means by the cam may be delayed or advanced.

13. A method of reducing the thickness of metal comprising passing the metal between two work rolls freely rotatably mounted upon the free ends of a pair of oscillatable arms which are pivotally mounted about pivotal axes one on each side of the metal pass line with their free ends and thus the work rolls in closer relationship than the pivotal axes of the arms, oscillating the arms in synchronism through a common plane in which the pivotal axes lie during passage of the metal between the work rolls so as to subject the metal to rolling action of the work rolls and thereby reduce the metal thickness, wherein the improvement comprises applying an auxiliary load to influence the roll displacement force during arm oscillation, the auxiliary load being applied or varied dependent upontthe oscillatory position of the arm on the outgoing side of the common plane in relation to the direction of movement of metal between the rolls, whereby during at least part of the oscillation of the arms to reduce thickness of metal on said side of the plane, the work rolls are urged towards straight-line parallel movement. 

2. Apparatus according to claim 1 wherein the means for applying an auxiliary load comprises a fluid-operable means.
 3. Apparatus according to claim 2 wherein the fluid-operable means comprises a cylinder and piston assembly which is operably connected to parts of the apparatus, the cylinder and piston being relatively movable upon operation to apply the auxiliary load, and wherein fluid-pressurizing means is provided having an operating means, the fluid pressurizing means being operably connected to the cylinder and piston assembly to vary the fluid pressure acting within the cylinder upon operation of the operating means.
 4. Apparatus according to claim 1 wherein on each side of the pass line, the frame has two beams upon which an oscillatable arm is pivotally mounted, the apparatus also having a rigid framework with each beam pivotally mounted about a pivotal axis to the framework about an axis extending transversely of the pass line for metal and at a position spaced from the pivotal axis of its arm in the direction of feed of the metal, and each beam being pivotally movable about its pivotal axis upon change in roll displacement force, and in respect of each beam, a screw down device is provided which acts at another position of the beam between the beam and the rigid frame work, the auxiliary load-applying means comprising a fluid-operable cylinder and piston means operable to assist the action of the roll displacement force upon each beam, fluid-pressurizing means operably connected to the cylinder and piston means to vary fluid pressure acting within the cylinder, and operating means operably connected to the pressurizing means to actuate the pressurizing means.
 5. Apparatus according to claim 4 including means for increasing and decreasing the stiffness of the apparatus and thereby the resistance to displacement of the rolls away from their theoretical paths of oscillation, such displacement being caused by roll displacement force, said means being operable to increase stiffness during movement of the rolls towards said plane and in a direction opposite to that of the direction of feed of metal to be passed between the rolls, and being operable to decrease the stiffness during movement of the rolls away from said plane and in the direction of metal feed, and wherein the fluid-pressurizing means is actuable by the Operating means to cause an application of or increase in the auxiliary load before the stiffness of the apparatus has been increased to its maximum by operation of the stiffness increasing and decreasing means.
 6. Apparatus according to claim 5 wherein with regard to each beam the stiffness increasing and decreasing means comprises at least one tubular member located so as to be subjected to roll displacement force during arm oscillation, increase in the roll displacement force causing pivotal movement of the beam accompanied by axial compression of the tubular member, and in which the cylinder and piston means are disposed so as to apply an auxiliary load to assist in the axial compression of the tubular member.
 7. Apparatus according to claim 6 wherein the screw down device comprises a screw-threaded hollow shaft and a screw-threaded nut received around the shaft, and wherein the tubular member is disposed axially within the shaft to axially receive the whole of the roll displacement force acting through the beam which then passes into the hollow shaft and under a certain degree of axial compression of the tubular member of the roll displacement force is transmitted directly into the tubular member and also into the hollow shaft to increase the stiffness of the apparatus, and the cylinder and piston means comprises a piston received within a cylinder which is disposed at one end of the tubular member, the piston having a tie rod extending along the tubular member and being operable upon the other end of the tubular member to apply an auxiliary load to assist in the axial compression of the tubular member while the whole of the roll displacement force is transmitted through the tubular member and then into the hollow shaft.
 8. Apparatus according to claim 4 wherein each beam of each arm lies in opposition to a beam of the other arm and the fluid-operable cylinder and piston means comprises two cylinder and piston assemblies each disposed between opposing beams of the arms to apply an auxiliary load between the arms to assist in pivotally moving them apart.
 9. Apparatus according to claim 8 wherein an accumulator containing fluid is connected with the interior of the cylinder of each assembly to maintain a desired pressure within the cylinder before the application of auxiliary load in the event of voliometric change within the cylinder caused by adjustment in operating positions of parts of the apparatus.
 10. Apparatus according to claim 2 wherein the operating means comprises a cam operably connected to the fluid-pressurizing means, the cam being secured to a rotatable shaft drivable by driving means.
 11. Apparatus according to claim 10 wherein means are provided for adjusting the operation of the fluid-pressurizing means to occur at any of a plurality of oscillatory positions of the arms.
 12. Apparatus according to claim 11 wherein said means for adjusting the operation of the fluid-pressurizing means comprises a gear means which is operably connected to the fluid-pressurizing means to alter its angular position relative to the axis of rotation of the cam whereby the operation of the fluid-pressurizing means by the cam may be delayed or advanced.
 13. A method of reducing the thickness of metal comprising passing the metal between two work rolls freely rotatably mounted upon the free ends of a pair of oscillatable arms which are pivotally mounted about pivotal axes one on each side of the metal pass line with their free ends and thus the work rolls in closer relationship than the pivotal axes of the arms, oscillating the arms in synchronism through a common plane in which the pivotal axes lie during passage of the metal between the work rolls so as to subject the metal to rolling action of the work rolls and thereby reduce the metal thickness, wherein the improvement comprises applying an auxiliary load to influence the roll displacement force during arm oscillation, the auxiliary load being applied or varied dependent upon the oscillatory position of the arm on the outgoing side of the common plane in relation to the direction of movement of metal between the rolls, whereby during at least part of the oscillation of the arms to reduce thickness of metal on said side of the plane, the work rolls are urged towards straight-line parallel movement. 